GENDER VARIATION IN BARTSIA ALPINA (SCROPHULARIACEAE), A SUBARCTIC PERENNIAL HERMAPHRODITE

Maternal and paternal effects on seed size and reproductive success (RS) were studied in a subarctic population of Bartsia alpina L. (Scrophulariaceae), a hemiparasitic perennial herb forming dense clones in open habitats. The impact of environmental factors was assessed in fertilization and defoliation experiments, and gender specialization of individual genets was investigated in a series of diallel experiments (reciprocal crossings) in the field. Maternal effects on seed weight were much larger than paternal effects, and seed weight was also strongly influenced by resource availability (especially nitrogen). The highest seed weights were usually found when genets were associated with Astragalus frigidus, which seems to be the optimal host species in the population, but similar results were achieved with NPK (nitrogen-phosphorus-potassium) fertilization. Defoliation experiments revealed an innate minimum seed weight, below which seed number was affected by resource deprivation. The reciprocal crossing program indicated a high level of gender specialization in individual genets (clones), ranging continuously from almost pure males to almost pure females. Early-flowering genets showed the highest average male RS, whereas female RS increased in late-flowering genets. Phenological separation of the genets into ‘early’ and ‘late’ revealed an inverse correlation between male and female performance. Numerous characters contributing to phenotypic gender were measured in the genets, but these characters and functional gender calculations from the diallel experiment were only weakly correlated. It is concluded that simultaneous measures of both male and female RS are needed for a reliable assessment of gender variation.